1. Field of the Invention
The present invention relates to a cushioning device, primarily for use in athletic equipment, comprised of a plurality of individual cells and a method of its manufacture. More particularly, this invention relates to a unique cushion comprised of an elastomeric body having a plurality of fluid filled individual cells, at least two cells being at different pressures. The method of manufacture of the invention provides the ability to form cushions having a plurality of cells at a plurality of pressures from a single fluid insertion point.
The cushion of the invention is particularly well-suited to be used as a portion of a sole in footwear. The cushion is especially beneficial in athletic footwear because the plurality of individual cells at different pressures facilitates the construction of a stable shoe capable of readily absorbing, distributing, and returning the frequent, repetitive, and intense forces experienced in sporting activities. While the invention will be described with particular reference to footwear, the inventive cushion is also recognized as suitable for other sports, and commercial and industrial related applications, including racquet handles, helmets, bicycle seats, gloves, automotive interiors, carpet padding, packaging material, medical and prosthetic devices, mattresses, clothing, braces, etc.
2. Description of the Art
Fluid filled cushions have been in existence for a very long time. U.S. Pat. No. 302,190 (1884), for example, describes one early attempt to fashion pneumatic cushioned footwear. However, until invention of the cushions described in U.S. Pat. Nos. 4,183,156 and 4,219,945, a commercially successful embodiment of fluid containing cushions for footwear was not readily available. These patents describe an inflated insert having multiple intercommunicating gas containing chambers which provide fluid support of the sole of a foot in a comfortable and efficient manner. In fact, these fluid containing cushioning devices are generally considered superior shock absorbing members which protect the bones, muscles, and ligaments of the foot and leg and the various body organs during walking, jumping, and running.
In attempts to improve on the technology disclosed in these patents, it has often been considered an advantage to construct the fluid containing footwear cushion from a plurality of non-communicating chambers. A frequently cited advantage of non-communicating chambers is the continued functionality of the unit upon puncture of an individual chamber. In this regard, Taiwanese Utility Model No. 33,544 describes a stacked arrangement of air cushions having two inflation points to facilitate separate inflation of peripheral air chambers and central air units. In this manner, puncture of one cell does not completely destroy the cushion's functionality.
In addition, it has been recognized that cushions comprised of non-communicating chambers at different pressures provide significant benefits to the wearer. In this regard, the geometry of the foot and the anatomic load support requirements for the foot are constantly changing in any activity that involves foot motion. Regardless of the activity and the change in geometry, there exists an optimum interaction between the foot and footwear which requires both good cushioning and also stabilization of the foot for effective and controlled movements, comfort, and to trigger the body's inherent automatic nerve/muscle proprioceptive reactions.
In general, footwear preferably functions to keep the foot properly and comfortably positioned, stabilized, and minimizes a tendency toward a medial and/or lateral rolling motion. In this regard, it has been recognized as desirable to construct a higher pressured periphery to the cushion to provide lateral stability and a lower pressured central portion, possibly of several inter-communicating cells, to provide greater deflection and shock absorbance.
For example, U.S. Pat. No. 5,353,459 describes a method of inflating a bladder comprised of at least a first and second distinct chamber. The chambers are linked in fluid communication by an interconnecting port with a fluid filled inlet in communication with the first chamber. The method comprises introducing a first pressurized fluid into the inlet to inflate the first and second chambers to a first predetermined pressure. The interconnecting port is then sealed to isolate the first chamber from the second chamber. Thereafter, the pressure is adjusted, the second chamber is pressurized, and the fluid inlet sealed.
Although this design provides a method of constructing a fluid filled cushion having non-communicating chambers at distinct pressures, certain limitations exist. Moreover, the process requires a plurality of pressurization adjustments and sequential sealing of the interconnecting ports to achieve a plurality of chambers at different pressures.
In contrast, the method of the present invention provides the ability to construct a cushion having a plurality of non-communicating cells at a plurality of different pressures in a single inflation step and optionally a single sealing step. In addition, the effectiveness of the method allows construction of a cushion having a significantly more complex geometric arrangement of pressurized cells than has previously been accomplished. Accordingly, a cushion having significantly improved energy return, shock absorbance, stability, durability, and longevity can be economically produced.